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Some surface characteristics due to center rest ball burnishing
Journal of Materials Processing Technology 167 (2005) 47–53
Some surface characteristics due to center rest ball burnishing M.H. El-Axira,∗ , A.A. Ibrahimb a
Department of Production Engineering and Mechanical Design, Faculty of Engineering, Shebin El-kom, Egypt b Department of Mechanical Engineering, Faculty of Engineering, Zagazig University, Shoubra, Egypt Received 27 August 2003; received in revised form 9 September 2004; accepted 15 September 2004
Abstract Lathe is one of machine tools used to produce round mechanical parts. Most of these parts must be finished with high accuracy, which cannot be obtained with conducting turning process only. The main objective of this work is how the moving rest can be used to finish the round-machined parts with high accuracy. To achieve the object, three ball burnishing tools are designed and constructed as long as replacing the three original adjustable jaws of the moving rest. Experimental work was carried out on a lathe to study the effect of this new burnishing tool and the lathe parameters, such as burnishing speed, burnishing force, and burnishing feed on some surface characteristics which are surface roughness, surface roundness, and reduction of diameter. The results showed that good surface characteristics can be obtained by using this tool with minimum cost by transferring the center rest from only support element to super finish tool (burnishing tool). Burnishing force and burnishing feed are the most important parameters that play an important role in controlling the values of all surface characteristics. © 2004 Elsevier B.V. All rights reserved. Keywords: Burnishing; Center rest; Surface roughness; Surface roundness
1. Introduction During recent years, considerable attention is being paid to the post-machining metal finishing operations, such as burnishing, which improves the surface characteristics by plastic deformation of the surface layers [1]. Burnishing is a cold-forming process, in which the metal near a machined surface is displaced from protrusion to fill the depressions. Besides producing a good surface finish, the burnishing process has additional advantages over other machining processes, such as increased hardness, corrosion resistance, and fatigue life as a result of the producing compressive residual stress. A literature survey shows that work on the burnishing process has been conducted by many researchers and the process also improves the properties of the parts, for instance, increased hardness [2–9], surface quality [2,7–12], larger maximum residual stress in compression [2,13,14], higher wear ∗
Corresponding author. E-mail addresses: [email protected] (M.H. El-Axir), [email protected] (A.A. Ibrahim). 0924-0136/$ – see front matter © 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.jmatprotec.2004.09.078
resistance [15–17], and better roundness [18]. The parameters affecting the surface finish are: burnishing force, feed, ball or roller material, number of passes, workpiece material, and lubrication [2]. The present paper examines the use of a new ball burnishing tool (center rest burnishing tool) to give good surface characteristics, such as higher surface finish, better roundness, and the smaller change of workpiece diameter that play an important role on the required tolerance and fit especially during assembly. The effects of three burnishing parameters (burnishing speed, feed, and burnishing force) on three different responses (surface roughness, roundness, and change in the workpiece diameter) are comprehensively studied.
2. Experimental work 2.1. Workpiece material In this work, mild steel was used as a workpiece material. The chemical composition and mechanical properties of the materials are displayed in Tables 1 and 2 .
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Table 1 Chemical composition %C %S %Mn %P %S
2.3. Burnishing conditions 0.25 0.25 0.55 0.045 0.045
Table 2 Mechanical properties σ u (N/cm2 ) σ y+ (N/cm2 ) BHN
450 230 130
σ u : ultimate stress, σ y+ : yield stress, and BHN: Breinl hardness number.
This material was selected because of its importance in industry and its susceptibility to surface and subsurface damage during burnishing. 2.2. Workpiece preparation The material was received in the form of solid bars. The dimensions of workpieces are shown in Fig. 1. The workpieces were prepared with three recesses such that each specimen could be used in three different conditions at positions to study the effect of the number of balls, which were used during burnishing using the moving rest burnishing tool: one ball for part A, two balls for part B, and three balls for part C. Furthermore, a portion D was left without burnishing for comparison purposes with portions A, B, and C. The part E is safety length to avoid the impact of the rest on the chuck. Fig. 2a shows a specimen attached to the chuck and the moving rest burnishing tool while Fig. 2b shows a tool of three balls, which are designed and constructed to replace the three original adjustable jaws of the steady rest. As shown in Fig. 2, each burnishing tool is ended with a hexagonal nut. By tightening this nut with torque arm wrench variable burnishing forces were obtained. In addition, burnishing with one, two, and three balls can be achieved by disabling one or two balls. The center rest was clamped with the lathe saddle to move with it as one part, and then variable feed rates for burnishing were applied by the lathe saddle.
Fig. 1. Workpiece geometry, dimensions in mm.
In this work, external moving rest ball burnishing tests were performed. All of the burnishing tests were performed under lubricated conditions. The lubrication was supplied through the ordinary lathe cooling system. Only three burnishing parameters were chosen, namely burnishing speed (V), burnishing force (F), and feed (f). Other parameters, such as ball diameter and lubrication were held constant throughout the work. Since dry burnishing conditions produced poor surface finish, it was decided to apply suitable soluble oil during all tests. It was emulation-type soluble oil mixed with water. Also, a constant ball diameter of 10 mm was used throughout this investigation. The burnishing conditions are summarized in Table 3. 2.4. Measurements In this work, produced surface roughness, change in workpiece diameter, and out-of-roundness were carefully measured using standard techniques. Different burnishing forces were applied using the torque arm key. Different feeds also were applied using lathes feeds as the center rest was clamped to move with the lathe saddle as one part. 2.4.1. Surface roughness Surface finish affects wear resistant, load bearing capacity, and corrosion resistance of the surface of the component. During burnishing process the tool compresses the outer surface layer by the polished hardened tool (ball or roller) so that it reduces the surface roughness. A Talysurf 402 series178 was used for measuring the surface roughness (measured by Ra) after burnishing. It should be pointed out here that the average of three readings for each portion (A, B, C, and D) of the specimens was calculated. 2.4.2. Change in the workpiece diameter Ball burnishing process usually reduced the diameter workpiece. The change in the workpiece was measured at different places using a micrometer with 0.001 mm accuracy. 2.4.3. Surface out-of-roundness A roundness error is considered as one of the important geometrical errors for cylindrical components because it has negative effects on accuracy and other important factors, such as the filling machine elements and wear in rotating elements. Also, it is well known that only plastic deformation takes place in the surface during the burnishing process, which in turn, causes variation in the produced roundness. Therefore, surface roundness before and after burnishing was measured using ROUNDTEST RA-112-122. For better results, the arithmetic average of three readings has been calculated.
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Fig. 2. Burnishing tool and its attachment to the center rest. (a) A specimen attached to the chuck and moving rest burnishing tool, and (b) burnishing tool.
3. Results and discussion To study and discuss the effect of the input parameters on the three different responses, Figs. 3–11 are constructed showing the results of the effect of burnishing conditions in the cases of one, two, and three ball on the response with the same burnishing conditions on the same figure. It should be pointed out here that in the case of burnishing force, it was found that the results for the burnishing force 70 N and 100 N and also of 200 N and 230 N were very close. Therefore, only three levels of burnishing force (70 N, 150 N, and 230 N) were presented in each figure.
crease in burnishing speed leads, in general, to a decrease in surface roughness up to about 1 m/s. The burnished surface roughness starts increasing slightly with any increase in burnishing speed more than 1 m/s. This is partly due to the fact that the deforming action of the ball is smaller at high speed and partly due to the chatter that usually induces at high speed. In the case of applying two balls, there is an interaction between burnishing speed and feed on surface roughness. At low feed, the increment of burnishing speed first decreases the surface roughness reaching to the lower value and then surface roughness starts to increase with a further
3.1. Surface roughness 3.1.1. Burnishing speed The effect of burnishing speed on the surface roughness in the case of using one, two, and three balls can be assessed from Fig. 3. The results reveal that the effect of burnishing on the surface roughness in the three cases is not the same. In the case of using only one ball, it can be seen that an inTable 3 Summary of burnishing conditions range Burnishing speed (m/s) Burnishing force (N) Burnishing feed (mm/rev) Ball diameter (mm) Burnishing conditions
0.159–1.84 70–230 0.04–0.19 10 Lubricated
Fig. 3. Effect of burnishing speed on surface roughness at various feeds in case of using one, two, and three balls.
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Fig. 4. Effect of burnishing speed on surface roughness at various forces in case of using one, two, and three balls.
increase in burnishing speed. At high feed, an increase in burnishing speed leads to a decrease in the burnished surface roughness. In case of applying three balls, it can be seen for the various feeds, the surface roughness of the burnished surface increases with an increase in burnishing speed. Also, this figure shows that the range of resulting values of burnished surface roughness is smaller than that in the previous two cases. The deterioration of the surface roughness in the burnishing process at high burnishing speeds is believed to be caused by the chatter that results in instability of the burnishing tool across the workpiece surface. Fig. 4 shows the effect of burnishing speed on surface roughness at various burnishing forces in the three different cases of the applying balls. The general trend of the results in the three cases reveals that there is an interaction between burnishing speed and force. At low burnishing force, the burnished surface roughness decreases with an increase in burnishing speed up to about 1.5 m/s. At high and highest burnishing force, an increase in burnishing speed up to 1 m/s leads to a considerable improvement in surface roughness.
Fig. 5. Effect of burnishing feed on surface roughness at various forces in case of using one, two, and three balls.
Fig. 6. Effect of burnishing speed on surface roundness at various feeds in case of using one, two, and three balls.
Fig. 7. Effect of burnishing speed on surface roundness at various forces in case of using one, two, and three balls.
This is may be because the lubricant looses its effect due to the insufficient time for it to penetrate between the balls and the workpiece surfaces. It is better then to select low speeds because the deforming action of the burnishing tool is greater and metal flow is regular at low speed.
Fig. 8. Effect of burnishing feed on surface roundness at various forces in case of using on, two, and three balls.
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surface the stability of the tool is much better than that at the previous two cases and this leads to a reduction in the effectiveness of chatter.
Fig. 9. Effect of burnishing speed on change in workpiece diameter at various feeds in case of using one, two, and three balls.
Fig. 10. Effect of burnishing speed on change in workpiece diameter at various forces in case of using one, two, and three balls.
In the case of applying three balls, it can be seen that at low burnishing force (70 N) the surface roughness of the burnished surface increases with an increase in burnishing speed whereas at forces of 150 N and 230 N. The burnished surface roughness decreases considerably with an increase in burnishing speed. It is believed that when the three balls of the moving rest burnishing tool contact with the workpiece
Fig. 11. Effect of burnishing feed on change in workpiece diameter at various forces in case of using one, two, and three balls.
3.1.2. Burnishing feed The influence of the feed rate on the surface roughness is shown in Figs. 3 and 5 for various speeds and forces in the three different cases of the effect of number of balls. The roughness of burnished surface in the three different cases firstly decreases with an increase in feed up to 0.12 mm/rev and then it starts to increase slightly with a further increase in burnishing feed. This may be due to the change of the contact area between the ball and workpiece, which is dependent on the burnishing parameters especially at very low feed and low forces. 3.1.3. Burnishing force Figs. 4 and 5 show the effect of burnishing force on the surface roughness for different speed and feed, respectively. The best results in the three different cases were obtained at burnishing force of 150 N. Also, from these figures, it can be seen that burnishing force interacts with burnishing speed. At low force, an increase in burnishing speed up to 1.5 m/s results in a decrease in surface roughness. At high force, the burnished surface roughness increases with an increase in burnishing speed. By increasing the applied force, the bulge in front of the burnisher become very large and region of plastic deformation widens, and this damages the already burnished surface or increases the surface roughness. At high speed, the high surface roughness can be interpreted by the low deforming action of the balls and also because the lubricant loses its effect due to the insufficient time for it to penetrate between the balls and workpiece. It is recommended that to select low speeds because the deforming action of the burnishing tool is greater. 3.2. Surface roundness 3.2.1. Burnishing speed The effect of burnishing speed on the variation of out-ofroundness can be assessed from Figs. 6 and 7. From these figures, it can be seen that in the case of using one ball, as the burnishing speed increases the out-of-roundness decreases at any value of feed and/or force. However in the case of two balls, there is an interaction between burnishing speed and feed. At low feed, an increase in burnishing speed leads to a decrease in the out-of-roundness whereas at highest feed the out-of-roundness increases with an increase in burnishing speed. The best results can be obtained at a combination of burnishing speed of 1 m/s with burnishing feed of 0.12 mm/rev. 3.2.2. Burnishing feed Figs. 6 and 8 present the effect of the burnishing feed on the burnished surface roundness at various speeds and forces, respectively. It can generally be seen that out-of-roundness
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decreases with an increase in burnishing feed, reaching a minimum value at a burnishing feed of 0.12 mm/rev. A further increase in feed causes an slight increase in out-of-roundness. From the results of these two figures that it is preferable, then, to avoid burnishing at very low feeds. This is because it may be at very low feed the deforming action of the balls is too high so that the flaking occurs at this very low feed.
surface. The increase in the change in diameter when employing high force can be attributed to the increase of the balls pressure on the workpiece surface. This results in compressing most asperities and increases the metal flow, which leads to the filling of more voids that exited in the subsurface layer due to machining operation (turning), or as a metal defect.
3.2.3. Burnishing force Burnishing force is one of the very important burnishing parameters that affect the results of this process. The increase in burnishing force causes increase in the amount of surface deformation as the tool passes along the surface of the workpiece. This will lead to an increase in the homogeneity of the surface layers, which have been affected by plastic deformation, so that the out-of-roundness will improve (decrease) via the increase in burnishing force up to 150 N, as shown in Fig. 8. The out-of-roundness of the burnished as burnishing force increased as a result of the regularity of the metal flow on the burnished surface from 70 N to 150 N. However, the results show that when burnishing mild steel with forces more than 150 N, the surface roundness is deteriorated. This may be because high forces cause shear failure in the subsurface layers, which in turn, results in the flaking.
4. Conclusion
3.3. Change in workpiece diameter 3.3.1. Burnishing speed Figs. 9 and 10 present the effect of the burnishing speed on the change in workpiece diameter at various feeds and forces, respectively. From these figures, it can be seen that for the various feed and force used in this work, a change in workpiece diameter decreases with an increase in burnishing speed. It is believed that the increase in the diameter change at low speed is possible due to the high deforming action of the ball of burnishing tool. 3.3.2. Burnishing feed Figs. 9 and 11 show the change in diameter versus burnishing feed for different burnishing speeds and forces, respectively. The change in diameter is considerable with an increase in burnishing feed from 0.04 mm/rev to 0.12 mm/rev. The maximum change in diameter is obtained at the lowest of burnishing feed and burnishing speed used in this work as a result of the significant effect of the ball burnishing tool on the outer burnished surface. The minimum change in the workpiece diameter was obtained in the case of employing the center rest burnishing tool with the three balls. 3.3.3. Burnishing force Burnishing force is one of the very important burnishing parameters that affect the results of this center rest burnishing tool. It can be seen form Figs. 10 and 11 that, for a given speed and/or feed, an increase in burnishing force causes an increase in change in workpiece diameter of the burnished
In this investigation, the center rest was used as a superfinishing tool by replacing the three original adjustable jaws of the center rest with three ball burnishing tool. The effects of burnishing parameters using this new tool were studied. The following can be concluded from the investigation: 1. The output responses of the burnished surface using the center rest ball burnishing are mainly influenced by the three parameters used. The burnishing force and burnishing speed play a major role and their effects are significant. 2. An increase in burnishing speed up to 1.5 m/s leads to a decrease in both the burnished surface roughness, out-ofroundness, and change in workpiece diameter whereas the increase in burnishing speed more than 1.5 m/s result in an increase in both surface roughness and out-of-roundness. 3. An increase in burnishing feed up to 0.12 mm/rev leads to a decrease in all responses studied in this work. The best results for surface roughness and/or roundness obtained at burnishing force of 150 N and burnishing feed of 0.12 mm/rev. 4. Good results for all responses studied in this work can be obtained using the center rest burnishing tool applying one ball or three balls.
References [1] N.H. Loh, S.C. Tam, S. Miyazawa, A study of the effects of ballburnishing parameters on surface roughness using factorial design, J. Mech. Working Technol. 18 (1989) 53–61. [2] M.H. El-Axir, An investigation into roller burnishing, Int. J. Mach. Tool Manuf. 40 (2000) 1603–1617. [3] M.M. El-Khabeery, M.H. El-Axir, Experimental techniques for studying the effects of milling roller-burnishing parameters on surface integrity, Int. J. Mach Tool Manuf. 41 (2001) 1705–1719. [4] N.H. Loh, S.C. Tam, S. Miyazawa, Statistical analyses of the effects of ball burnishing parameters on surface hardness, Wear 129 (1989) 235. [5] I. Yashcheritsyn, E.I. Pyatosin, V.V. Votchuga, Hereditary influence of pre-treatment on roller-burnishing surface wear resistance, Soviet J. Friction Wear 8 (2) (1987) 87. [6] M. Fattouh, M.H. El-Axir, S.M. Serage, Investigation into the burnishing of external cylindrical surface of 70/30 Cu–Zn-alloy, Wear (1988) 127. [7] S.S.G. Lee, S.C. Tam, N.H. Loh, S. Miyazawa, An investigation into the ball burnishing of an AISI 1045 free-form surface, J. Mater. Process. Technol. 29 (1992) 203. [8] A.M. Hassan, The effects of ball- and roller-burnishing on the surface roughness and hardness of some non-ferrous metals, J. Mater. Process. Technol. 72 (1997) 385.
M.H. El-Axir, A.A. Ibrahim / Journal of Materials Processing Technology 167 (2005) 47–53 [9] A.M. Hassan, A.S. Al-Bsharat, Improvements in some properties of non-ferrous metals by the application of the ball burnishing process, J. Mater. Process. Technol. 59 (1996) 250. [10] S.S.G. Lee, S.C. Tam, N.H. Loh, Ball burnishing of 316L stainless steel, J. Mater. Process. Technol. 37 (1993) 241. [11] A.M. Hassan, A.S. Al-Bsharat, Influence of burnishing process on surface roughness, hardness, and microstructure of some non-ferrous metals, Wear 199 (1996) 1–8. [12] A.M. Hassan, H.F. Al-Jalil, A.A. Ebied, Burnishing force and number of ball passes for the optimum surface finish of brass components, J. Mater. Process. Technol. 83 (1998) 176. [13] M. Fattouh, M.M. El-Khabeery, Residual stress distribution in burnishing solution treated and aged 7075 aluminum alloy, Int. J. Mach. Tool Manuf. 29 (1) (1989) 153.
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[14] F. Klocke, J. Liermamnn, Roller burnishing of hard turned surface, Int. J. Mach. Tool Manuf. 38 (5-6) (1998) 419. [15] A.N. Niberg, Wear resistance of sideways strengthened by burnishing, Soviet Eng. Res. 7 (5) (1987) 67. [16] P.C. Michael, N. Saka, E. Rabinowicz, Burnishing and adhesive wear of an electrically conductive polyester-carbon film, Wear 132 (1989) 265. [17] A.M. Hassan, A.-D. Sulieman, Improvement in the wear resistance of brass components by the ball burnishing process, J. Mater. Process. Technol. 96 (November (1–3)) (1999) 73–80. [18] M.H. El-Axir, M.M. El-Khabeery, Influence of orthogonal burnishing parameters on surface characteristics for various materials, J. Mater. Process. Technol. 132 (2003) 82–89.
Some surface characteristics due to center rest ball burnishing M.H. El-Axira,∗ , A.A. Ibrahimb a
Department of Production Engineering and Mechanical Design, Faculty of Engineering, Shebin El-kom, Egypt b Department of Mechanical Engineering, Faculty of Engineering, Zagazig University, Shoubra, Egypt Received 27 August 2003; received in revised form 9 September 2004; accepted 15 September 2004
Abstract Lathe is one of machine tools used to produce round mechanical parts. Most of these parts must be finished with high accuracy, which cannot be obtained with conducting turning process only. The main objective of this work is how the moving rest can be used to finish the round-machined parts with high accuracy. To achieve the object, three ball burnishing tools are designed and constructed as long as replacing the three original adjustable jaws of the moving rest. Experimental work was carried out on a lathe to study the effect of this new burnishing tool and the lathe parameters, such as burnishing speed, burnishing force, and burnishing feed on some surface characteristics which are surface roughness, surface roundness, and reduction of diameter. The results showed that good surface characteristics can be obtained by using this tool with minimum cost by transferring the center rest from only support element to super finish tool (burnishing tool). Burnishing force and burnishing feed are the most important parameters that play an important role in controlling the values of all surface characteristics. © 2004 Elsevier B.V. All rights reserved. Keywords: Burnishing; Center rest; Surface roughness; Surface roundness
1. Introduction During recent years, considerable attention is being paid to the post-machining metal finishing operations, such as burnishing, which improves the surface characteristics by plastic deformation of the surface layers [1]. Burnishing is a cold-forming process, in which the metal near a machined surface is displaced from protrusion to fill the depressions. Besides producing a good surface finish, the burnishing process has additional advantages over other machining processes, such as increased hardness, corrosion resistance, and fatigue life as a result of the producing compressive residual stress. A literature survey shows that work on the burnishing process has been conducted by many researchers and the process also improves the properties of the parts, for instance, increased hardness [2–9], surface quality [2,7–12], larger maximum residual stress in compression [2,13,14], higher wear ∗
Corresponding author. E-mail addresses: [email protected] (M.H. El-Axir), [email protected] (A.A. Ibrahim). 0924-0136/$ – see front matter © 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.jmatprotec.2004.09.078
resistance [15–17], and better roundness [18]. The parameters affecting the surface finish are: burnishing force, feed, ball or roller material, number of passes, workpiece material, and lubrication [2]. The present paper examines the use of a new ball burnishing tool (center rest burnishing tool) to give good surface characteristics, such as higher surface finish, better roundness, and the smaller change of workpiece diameter that play an important role on the required tolerance and fit especially during assembly. The effects of three burnishing parameters (burnishing speed, feed, and burnishing force) on three different responses (surface roughness, roundness, and change in the workpiece diameter) are comprehensively studied.
2. Experimental work 2.1. Workpiece material In this work, mild steel was used as a workpiece material. The chemical composition and mechanical properties of the materials are displayed in Tables 1 and 2 .
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Table 1 Chemical composition %C %S %Mn %P %S
2.3. Burnishing conditions 0.25 0.25 0.55 0.045 0.045
Table 2 Mechanical properties σ u (N/cm2 ) σ y+ (N/cm2 ) BHN
450 230 130
σ u : ultimate stress, σ y+ : yield stress, and BHN: Breinl hardness number.
This material was selected because of its importance in industry and its susceptibility to surface and subsurface damage during burnishing. 2.2. Workpiece preparation The material was received in the form of solid bars. The dimensions of workpieces are shown in Fig. 1. The workpieces were prepared with three recesses such that each specimen could be used in three different conditions at positions to study the effect of the number of balls, which were used during burnishing using the moving rest burnishing tool: one ball for part A, two balls for part B, and three balls for part C. Furthermore, a portion D was left without burnishing for comparison purposes with portions A, B, and C. The part E is safety length to avoid the impact of the rest on the chuck. Fig. 2a shows a specimen attached to the chuck and the moving rest burnishing tool while Fig. 2b shows a tool of three balls, which are designed and constructed to replace the three original adjustable jaws of the steady rest. As shown in Fig. 2, each burnishing tool is ended with a hexagonal nut. By tightening this nut with torque arm wrench variable burnishing forces were obtained. In addition, burnishing with one, two, and three balls can be achieved by disabling one or two balls. The center rest was clamped with the lathe saddle to move with it as one part, and then variable feed rates for burnishing were applied by the lathe saddle.
Fig. 1. Workpiece geometry, dimensions in mm.
In this work, external moving rest ball burnishing tests were performed. All of the burnishing tests were performed under lubricated conditions. The lubrication was supplied through the ordinary lathe cooling system. Only three burnishing parameters were chosen, namely burnishing speed (V), burnishing force (F), and feed (f). Other parameters, such as ball diameter and lubrication were held constant throughout the work. Since dry burnishing conditions produced poor surface finish, it was decided to apply suitable soluble oil during all tests. It was emulation-type soluble oil mixed with water. Also, a constant ball diameter of 10 mm was used throughout this investigation. The burnishing conditions are summarized in Table 3. 2.4. Measurements In this work, produced surface roughness, change in workpiece diameter, and out-of-roundness were carefully measured using standard techniques. Different burnishing forces were applied using the torque arm key. Different feeds also were applied using lathes feeds as the center rest was clamped to move with the lathe saddle as one part. 2.4.1. Surface roughness Surface finish affects wear resistant, load bearing capacity, and corrosion resistance of the surface of the component. During burnishing process the tool compresses the outer surface layer by the polished hardened tool (ball or roller) so that it reduces the surface roughness. A Talysurf 402 series178 was used for measuring the surface roughness (measured by Ra) after burnishing. It should be pointed out here that the average of three readings for each portion (A, B, C, and D) of the specimens was calculated. 2.4.2. Change in the workpiece diameter Ball burnishing process usually reduced the diameter workpiece. The change in the workpiece was measured at different places using a micrometer with 0.001 mm accuracy. 2.4.3. Surface out-of-roundness A roundness error is considered as one of the important geometrical errors for cylindrical components because it has negative effects on accuracy and other important factors, such as the filling machine elements and wear in rotating elements. Also, it is well known that only plastic deformation takes place in the surface during the burnishing process, which in turn, causes variation in the produced roundness. Therefore, surface roundness before and after burnishing was measured using ROUNDTEST RA-112-122. For better results, the arithmetic average of three readings has been calculated.
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Fig. 2. Burnishing tool and its attachment to the center rest. (a) A specimen attached to the chuck and moving rest burnishing tool, and (b) burnishing tool.
3. Results and discussion To study and discuss the effect of the input parameters on the three different responses, Figs. 3–11 are constructed showing the results of the effect of burnishing conditions in the cases of one, two, and three ball on the response with the same burnishing conditions on the same figure. It should be pointed out here that in the case of burnishing force, it was found that the results for the burnishing force 70 N and 100 N and also of 200 N and 230 N were very close. Therefore, only three levels of burnishing force (70 N, 150 N, and 230 N) were presented in each figure.
crease in burnishing speed leads, in general, to a decrease in surface roughness up to about 1 m/s. The burnished surface roughness starts increasing slightly with any increase in burnishing speed more than 1 m/s. This is partly due to the fact that the deforming action of the ball is smaller at high speed and partly due to the chatter that usually induces at high speed. In the case of applying two balls, there is an interaction between burnishing speed and feed on surface roughness. At low feed, the increment of burnishing speed first decreases the surface roughness reaching to the lower value and then surface roughness starts to increase with a further
3.1. Surface roughness 3.1.1. Burnishing speed The effect of burnishing speed on the surface roughness in the case of using one, two, and three balls can be assessed from Fig. 3. The results reveal that the effect of burnishing on the surface roughness in the three cases is not the same. In the case of using only one ball, it can be seen that an inTable 3 Summary of burnishing conditions range Burnishing speed (m/s) Burnishing force (N) Burnishing feed (mm/rev) Ball diameter (mm) Burnishing conditions
0.159–1.84 70–230 0.04–0.19 10 Lubricated
Fig. 3. Effect of burnishing speed on surface roughness at various feeds in case of using one, two, and three balls.
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Fig. 4. Effect of burnishing speed on surface roughness at various forces in case of using one, two, and three balls.
increase in burnishing speed. At high feed, an increase in burnishing speed leads to a decrease in the burnished surface roughness. In case of applying three balls, it can be seen for the various feeds, the surface roughness of the burnished surface increases with an increase in burnishing speed. Also, this figure shows that the range of resulting values of burnished surface roughness is smaller than that in the previous two cases. The deterioration of the surface roughness in the burnishing process at high burnishing speeds is believed to be caused by the chatter that results in instability of the burnishing tool across the workpiece surface. Fig. 4 shows the effect of burnishing speed on surface roughness at various burnishing forces in the three different cases of the applying balls. The general trend of the results in the three cases reveals that there is an interaction between burnishing speed and force. At low burnishing force, the burnished surface roughness decreases with an increase in burnishing speed up to about 1.5 m/s. At high and highest burnishing force, an increase in burnishing speed up to 1 m/s leads to a considerable improvement in surface roughness.
Fig. 5. Effect of burnishing feed on surface roughness at various forces in case of using one, two, and three balls.
Fig. 6. Effect of burnishing speed on surface roundness at various feeds in case of using one, two, and three balls.
Fig. 7. Effect of burnishing speed on surface roundness at various forces in case of using one, two, and three balls.
This is may be because the lubricant looses its effect due to the insufficient time for it to penetrate between the balls and the workpiece surfaces. It is better then to select low speeds because the deforming action of the burnishing tool is greater and metal flow is regular at low speed.
Fig. 8. Effect of burnishing feed on surface roundness at various forces in case of using on, two, and three balls.
M.H. El-Axir, A.A. Ibrahim / Journal of Materials Processing Technology 167 (2005) 47–53
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surface the stability of the tool is much better than that at the previous two cases and this leads to a reduction in the effectiveness of chatter.
Fig. 9. Effect of burnishing speed on change in workpiece diameter at various feeds in case of using one, two, and three balls.
Fig. 10. Effect of burnishing speed on change in workpiece diameter at various forces in case of using one, two, and three balls.
In the case of applying three balls, it can be seen that at low burnishing force (70 N) the surface roughness of the burnished surface increases with an increase in burnishing speed whereas at forces of 150 N and 230 N. The burnished surface roughness decreases considerably with an increase in burnishing speed. It is believed that when the three balls of the moving rest burnishing tool contact with the workpiece
Fig. 11. Effect of burnishing feed on change in workpiece diameter at various forces in case of using one, two, and three balls.
3.1.2. Burnishing feed The influence of the feed rate on the surface roughness is shown in Figs. 3 and 5 for various speeds and forces in the three different cases of the effect of number of balls. The roughness of burnished surface in the three different cases firstly decreases with an increase in feed up to 0.12 mm/rev and then it starts to increase slightly with a further increase in burnishing feed. This may be due to the change of the contact area between the ball and workpiece, which is dependent on the burnishing parameters especially at very low feed and low forces. 3.1.3. Burnishing force Figs. 4 and 5 show the effect of burnishing force on the surface roughness for different speed and feed, respectively. The best results in the three different cases were obtained at burnishing force of 150 N. Also, from these figures, it can be seen that burnishing force interacts with burnishing speed. At low force, an increase in burnishing speed up to 1.5 m/s results in a decrease in surface roughness. At high force, the burnished surface roughness increases with an increase in burnishing speed. By increasing the applied force, the bulge in front of the burnisher become very large and region of plastic deformation widens, and this damages the already burnished surface or increases the surface roughness. At high speed, the high surface roughness can be interpreted by the low deforming action of the balls and also because the lubricant loses its effect due to the insufficient time for it to penetrate between the balls and workpiece. It is recommended that to select low speeds because the deforming action of the burnishing tool is greater. 3.2. Surface roundness 3.2.1. Burnishing speed The effect of burnishing speed on the variation of out-ofroundness can be assessed from Figs. 6 and 7. From these figures, it can be seen that in the case of using one ball, as the burnishing speed increases the out-of-roundness decreases at any value of feed and/or force. However in the case of two balls, there is an interaction between burnishing speed and feed. At low feed, an increase in burnishing speed leads to a decrease in the out-of-roundness whereas at highest feed the out-of-roundness increases with an increase in burnishing speed. The best results can be obtained at a combination of burnishing speed of 1 m/s with burnishing feed of 0.12 mm/rev. 3.2.2. Burnishing feed Figs. 6 and 8 present the effect of the burnishing feed on the burnished surface roundness at various speeds and forces, respectively. It can generally be seen that out-of-roundness
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decreases with an increase in burnishing feed, reaching a minimum value at a burnishing feed of 0.12 mm/rev. A further increase in feed causes an slight increase in out-of-roundness. From the results of these two figures that it is preferable, then, to avoid burnishing at very low feeds. This is because it may be at very low feed the deforming action of the balls is too high so that the flaking occurs at this very low feed.
surface. The increase in the change in diameter when employing high force can be attributed to the increase of the balls pressure on the workpiece surface. This results in compressing most asperities and increases the metal flow, which leads to the filling of more voids that exited in the subsurface layer due to machining operation (turning), or as a metal defect.
3.2.3. Burnishing force Burnishing force is one of the very important burnishing parameters that affect the results of this process. The increase in burnishing force causes increase in the amount of surface deformation as the tool passes along the surface of the workpiece. This will lead to an increase in the homogeneity of the surface layers, which have been affected by plastic deformation, so that the out-of-roundness will improve (decrease) via the increase in burnishing force up to 150 N, as shown in Fig. 8. The out-of-roundness of the burnished as burnishing force increased as a result of the regularity of the metal flow on the burnished surface from 70 N to 150 N. However, the results show that when burnishing mild steel with forces more than 150 N, the surface roundness is deteriorated. This may be because high forces cause shear failure in the subsurface layers, which in turn, results in the flaking.
4. Conclusion
3.3. Change in workpiece diameter 3.3.1. Burnishing speed Figs. 9 and 10 present the effect of the burnishing speed on the change in workpiece diameter at various feeds and forces, respectively. From these figures, it can be seen that for the various feed and force used in this work, a change in workpiece diameter decreases with an increase in burnishing speed. It is believed that the increase in the diameter change at low speed is possible due to the high deforming action of the ball of burnishing tool. 3.3.2. Burnishing feed Figs. 9 and 11 show the change in diameter versus burnishing feed for different burnishing speeds and forces, respectively. The change in diameter is considerable with an increase in burnishing feed from 0.04 mm/rev to 0.12 mm/rev. The maximum change in diameter is obtained at the lowest of burnishing feed and burnishing speed used in this work as a result of the significant effect of the ball burnishing tool on the outer burnished surface. The minimum change in the workpiece diameter was obtained in the case of employing the center rest burnishing tool with the three balls. 3.3.3. Burnishing force Burnishing force is one of the very important burnishing parameters that affect the results of this center rest burnishing tool. It can be seen form Figs. 10 and 11 that, for a given speed and/or feed, an increase in burnishing force causes an increase in change in workpiece diameter of the burnished
In this investigation, the center rest was used as a superfinishing tool by replacing the three original adjustable jaws of the center rest with three ball burnishing tool. The effects of burnishing parameters using this new tool were studied. The following can be concluded from the investigation: 1. The output responses of the burnished surface using the center rest ball burnishing are mainly influenced by the three parameters used. The burnishing force and burnishing speed play a major role and their effects are significant. 2. An increase in burnishing speed up to 1.5 m/s leads to a decrease in both the burnished surface roughness, out-ofroundness, and change in workpiece diameter whereas the increase in burnishing speed more than 1.5 m/s result in an increase in both surface roughness and out-of-roundness. 3. An increase in burnishing feed up to 0.12 mm/rev leads to a decrease in all responses studied in this work. The best results for surface roughness and/or roundness obtained at burnishing force of 150 N and burnishing feed of 0.12 mm/rev. 4. Good results for all responses studied in this work can be obtained using the center rest burnishing tool applying one ball or three balls.
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